European Patent EP 1 203 510 to Nielsen et al. discloses a method of canceling feedback in an acoustic system, such as a hearing aid. An acoustic signal is received by a microphone, amplified and filtered in an amplifier and subsequently transmitted by a speaker. A portion of the speaker output undesirably returns to the microphone via an acoustic feedback path, e.g. through a vent in the hearing aid. The microphone thus outputs a feedback signal along with the signal received from the environment. The microphone, the amplifier, the speaker and the feedback path together form a feedback loop. Depending on gains and phase shifts in the feedback loop, audible artifacts, such as whistles, may be generated. In order to suppress such artifacts that may be very annoying to e.g. a user of a hearing aid, the input to the speaker is also fed to an adaptive filter, which emulates the portion of the feedback loop formed by the speaker, the feedback path and the microphone. The output of the adaptive filter is thus an estimate of the feedback signal, and in order to cancel the feedback, the estimated feedback signal is subtracted from the microphone output before it is fed to the amplifier. Thus, ideally, only the signal received from the environment reaches the amplifier. The transfer function of the adaptive filter is controlled by a set of filter coefficients, which is updated repeatedly using a so-called least-mean-square (LMS) algorithm as already well known in the art. The LMS algorithm receives a delayed version of the speaker input as a reference signal and the amplifier input as an error signal and attempts to determine the filter coefficients so that the estimated feedback signal resembles the actual feedback signal. The delay ideally corresponds to the delay in the emulated portion of the feedback loop. The disclosed invention solves the problem that the stability of the feedback loop emulation decreases when the microphone receives signals with long autocorrelation functions from the environment, e.g. low-frequency (LF) tones. The disclosed invention achieves its object by feeding only a high-frequency (HF) range of the reference and error signals to the algorithm. The HF range preferably includes those frequency ranges, in which feedback-caused artifacts are expected to occur. In order to avoid a deterioration of the filter characteristic in the remaining LF range, the LF range of the reference signal is replaced with an LF noise signal, and the LF range of the error signal is permanently set to zero.